During a process that a system of a User Generated Content (User Generated Content, UGC) service (such as a microblogging) changes from an original system to a new one, data migration issues are unavoidably to be encountered. How to migrate data completely from the original system to the new system without users' awareness as far as possible is always a problem pressing for solutions.
In a conventional data migration process, data in the original system is imported to a new system after writes to the original system are disabled, and then write requests of users are routed to the new system to continue the service. However, such a data migration process is most violent, in which writes to the original system must be disabled, and how long the writes are disabled depends on the time consumed by the data migration. The more time the data migration needs, the longer the writes must be disabled, thereby affecting write requests of users.